Chemical Engineering September 2023 - 34

De Nora
CASE STUDY
A manufacturing facility in West Virginia
was dealing with the following two issues:
1. An effluent with a toxicity level that
needed to be reduced by 50% to meet
state requirements for groundwater
discharge compliance
2. High costs for disposing of biological
sludge
FIGURE 2. Ozone generators are used to produce O3 gas that can be used to eliminate contaminants of
concern from wastewater streams
or high total organic carbon (TOC)
content, when peroxide quenching is
a concern or if a plant requires the
application of ozone for additional
reasons, such as the mitigation of
pharmaceutical micropollutants.
Ultraviolet AOP treatment
UV light alters the DNA of harmful
organisms without the use of
chemicals, rendering pathogens unable
to reproduce and cause harm.
UV affects waterborne pathogens
that can infect humans, including
protozoa, such as Cryptosporidium
parvum and Giardia lamblia; viruses
such as poliovirus and hepatitis A;
and bacteria, such as Salmonella
typhi, Shigella, Escherichia coli and
Vibrio cholera.
UV AOP is also proven effective
at inactivating 1,4-dioxane, as well
as other harmful contaminants frequently
discovered in wastewater,
such
as N-nitrosodimethylamine
(NDMA). There are essentially two
kinds of UV AOP: UV plus hydrogen
peroxide; and UV plus chlorine.
With UV/peroxide, hydroxyl radicals
are generated by the photolysis
of hydrogen peroxide. During photolysis,
the energy of the UV photon
splits the hydrogen peroxide into two
hydroxyl radicals, which are highly
unstable and react within microseconds
with contaminants in the water.
The hydrogen peroxide is dosed
and mixed in ahead of the UV reactor,
and after photolysis, the treated
water is released in the effluent.
34
With UV/chlorine, the chlorine dissolves
in water to form hypochlorous
acid (HOCl), which dissociates to
form OCl- at high pH - the higher
the pH, the more OCl- is formed.
Both treatment methods absorb
UV and form hydroxyl radicals, but
OCl- is a significant hydroxyl scavenger,
so even in small amounts, it
can render the UV/chlorine process
less efficient than using UV/peroxide.
For this reason, UV/chlorine is used
more often when the pH is lower,
such as in potable reuse AOP where
the pH of the reverse-osmosis (RO)
permeate is normally less than 6.
AOP and 1,4-dioxane
Simply put, AOP is the best technology
for treatment of 1,4-dioxane.
The hydroxyl radicals generated by
AOP are powerful oxidants that react
with 1,4-dioxane contaminants and
render them harmless. It is the most
technically and economically
feasible
solution
with
for
granular
De Nora
treatment,
because 1,4-dioxane
is very soluble in water
and therefore not effectively
treated
activated
carbon (GAC) or air
stripping. Additionally, 1,4-dioxane
will even pass through
RO membranes,
so AOP
represents the most suitable
treatment solution.
Toxicity testing protocols
Any industrial facility that
discharges water directly
FIGURE 3. Before permanently installing a water-treatment
system, it is helpful to vet the technology using an onsite
pilot-scale skid system
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SEPTEMBER 2023
The site needed a disposal solution that
could integrate with their existing plant, and
they needed guidance on treatment strategies.
Granular activated carbon (GAC)
was considered, but rejected, due to high
operating cost. UV was not applicable due
to low UV transmittance and high organics
content. The facility ultimately decided
to pilot an ozone AOP treatment system.
Among several reasons, ozone AOP was
selected for its ability to oxidize the majority
of the molecules causing toxicity,
including surfactants, phenols, hydrocarbons,
cyanide, pharmaceutical micropollutants,
1,4-dioxane and others.
The system dramatically
reduced the
toxicity of the plant's effluent to as low as
0, far surpassing state regulatory requirements
and reducing the risk of fines and
litigation. Also, the plant will save between
$100,000 and $150,000 per year thanks
to a reduction in biological sludge disposal.
The pilot has now been converted
into a permanent installation.
❑
into U.S. waters - oceans, wetlands,
marshes, creeks, streams,
rivers and lakes - is subject to
oversight of the NPDES program
according to the Clean Water Act.
Part of this oversight requires that
facilities regularly perform Whole Effluent
Toxicity (WET) tests on their
wastewater effluent.
The WET test measures the effects
of facility wastewater on specific test
organisms - specifically, their ability
to survive, grow and reproduce. As

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Chemical Engineering September 2023

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